The invention is notably directed to a tunable resistive element.
The invention further concerns a related device comprising tunable resistive elements, a neuromorphic network comprising tunable resistive elements and a design structure.
Nanoscale memory devices, whose resistance depends on the history of the electric signals applied, could become critical building blocks in new computing paradigms, such as brain-inspired computing and in-memory computing.
One promising example for nanoscale memory devices are phase-change memory (PCM) devices. PCM is a non-volatile solid-state memory technology that exploits the reversible, thermally-assisted switching of phase-change materials, in particular chalcogenide compounds such as GST (Germanium-Antimony-Tellurium), between states with different electrical resistance. The fundamental storage unit (the “cell”) can be programmed into a number of different states, or levels, which exhibit different resistance characteristics. The programmable cell-states can be used to represent different data values, permitting storage of information.
Another one of the leading solutions is Resistive RAM (RRAM). It involves creating filaments of e.g. oxygen vacancies in dielectrics such as HfO2, using a process called soft breakdown. The filaments are subsequently closed (SET) or opened (RESET) during operation. Strongly reducing metals, e.g. titanium, may be used as one of the electrodes to enhance the formation of the filament. However, the SET process is rather local and abrupt, due to the filamentary nature of the switching and the difficulty to exchange oxygen with the electrode.
Energy efficient training of Artificial Neural Networks (ANNs) using back-propagation (BP) algorithm requires dedicated hardware. The front-up approach is to run matrix operations required for BP on a matrix of resistive elements with a metal-insulator-metal structure (MIM). The ideal characteristics for the resistive elements (G vs pulses) is symmetric.
Accordingly, there is a need for further improvements of resistive elements.